1. Field of the Invention
The present invention relates to an apparatus and method for plating the processing surface, to be plated, of a substrate, and more particularly to a plating apparatus and method suited for forming a plated film in fine trenches and plugs for interconnects, and in the openings of a resist formed in the surface of a substrate such as a semiconductor wafer, and for forming bumps (protruding electrodes) on the surface of a semiconductor wafer for electrically connecting semiconductor chips and the substrate.
2. Description of the Related Art
FIG. 30 shows the general construction of a conventional plating apparatus for plating copper or the like on a semiconductor substrate. As shown in FIG. 30, the conventional substrate plating apparatus is provided with a plating tank 411 that holds a plating liquid Q, and arranges a substrate W, such as a semiconductor wafer, and an anode 412 opposing each other therein. A plating power source 413 is connected to the substrate W and the anode 412. When the plating power source 413 applies a prescribed voltage thereacross, a current containing ions dissolved from the copper plate or the like serving as the anode 412 flows toward the surface (processing surface to be plated) of the substrate W and forms a plated copper film thereon. The substrate W is detachably held by a substrate holder 414. When the current flows between the anode 412, which is formed of copper containing phosphorus, for example, and the substrate W, the ionized copper is conveyed by the plating current and deposited on the surface of the substrate W to form a plated film. The plating liquid Q overflowing the wall 415 of the plating tank 411 is collected in a recovery tank 416. The plating liquid Q in the recovery tank 416 is reintroduced to the plating tank 411 through a plating liquid circulation system comprising a pump 420, a temperature regulating tank 421, a filter 422, a flow meter 423 and so on.
When forming a plated film in fine trenches and plugs for interconnects, or in openings of a resist having poor wettability formed in a substrate, such as a semiconductor water, a plating liquid or a pretreatment liquid cannot enter deep inside of the trenches, plugs and openings, thereby leaving air bubbles therein. Such air bubbles can cause plating defects or incomplete plating.
In order to prevent such plating defects or incomplete plating, conventionally the surface tension of a plating liquid has been lowered by adding a surfactant thereto, thereby facilitating entering of the plating liquid into the fine trenches and plugs for interconnects of the substrate to be plated, or the openings of a resist. However, air bubbles tend to generate more easily in a plating liquid during circulation when the surface tension of the plating liquid is low. Further, the addition of a surfactant to the plating liquid can cause an abnormal plating deposition and increase the amount of an organic substance taken in the plated film, leading to lowering of the properties of the plated film.
In a tape automated bonding (TAB) or flip chip, for example, it has been widely conducted to deposit gold, copper, solder, nickel or multi-layered materials thereof at prescribed areas (electrodes) on the surface of a semiconductor chip having interconnects, thereby forming protruding connecting electrodes (bumps). Such bumps electrically connect the semicondcutor chip with substrate electrodes or TAB electrodes. There are various methods for forming these bumps, including an electrolytic plating method, vapor deposition method, printing method, and ball bump method. The electrolytic plating method has become wide in use due to its relatively stable performance and capability of forming fine connections, in view of the recent tendency toward increasing the number of I/O terminals on semiconductor chips and toward finer pitch.
The electrolytic plating method includes a spurting or cup method in which a substrate such as a semicondcutor wafer is positioned horizontally with the processing surface to be plated facedown and a plating liquid is spurted from below and a dipping method in which the substrate is placed vertically in a plating tank and immersed in a plating liquid, while a plating liquid is supplied from the bottom of the plating tank and is allowed to overflow the tank. According to the dipping method of electrolytic plating, bubbles that can adversely affect the quality of the plating are easily removed and the footprint is small. Further, the dipping method can be readily adapted to variations in wafer size. The dipping method is therefore considered to be suited for bump plating in which holes to be filled by the plating are relatively large and which requires a fairly long plating time.
When forming bumps at prescribed areas of a substrate having interconnects, a seed layer 500 as an electric feed layer is first formed on the surface of the substrate W, as shown in FIG. 29A. A resist 502 having a height H of e.g. 20-120 μm is applied to the entire surface of the seed layer 500. An opening 502a having a diameter D of e.g. 20-200 μm is formed in a prescribed portion of the resist 502. Plating is performed onto such a surface of the substrate W to deposit and grow a plated film 504 in the opening 502a, thereby forming a bump 506 (see FIGS. 29B-29E). When using the facedown-type electrolytic plating to form the bump 506, air bubbles 508 generated in the plating liquid are likely to remain on the inside of the opening 502a, as shown by the dotted line in FIG. 29A, particularly when the resist 502 is hydrophobic.
When using the dipping-type electrolytic plating apparatus to form the bump, on the other hand, the air bubbles can escape easily. Conventional electrolytic plating apparatuses for the dipping method employ a substrate holder which holds a substrate sealing the edge and the backside thereof, such as a semiconductor wafer, while exposing the front surface (processing surface to be plated). Since such a substrate holder is immersed in the plating liquid with the substrate when plating the surface of the substrate, it is difficult to automate the entire plating process from loading of the substrate to unloading of the substrate after plating. Further, the plating apparatus occupies a considerably large space.